Stabilized power supply-use device, and switching power supply and electronic device using the same

ABSTRACT

A stabilized power supply-use device of the present invention, which is mounted on a switching power supply, is an IC into which power transistors, a control circuit for controlling a base current of the power transistors, and other electronic components are formed, and an overcurrent detecting resistor connected in series with the power transistor is realized by a resister provided externally to the IC. Therefore, as compared to the overcurrent detecting resistor being made up of aluminum wiring patterns inside the IC, the overcurrent detecting resistor of the present invention dramatically decreases variations in value of resistance, whereby it is possible to improve an accuracy of voltage detection and to arbitrarily set a value of resistance. This eliminates the need for a needlessly increased input power capacity in a test based on safety standard and other tests, thereby enabling a switching power supply manufactured at a lower cost.

FIELD OF THE INVENTION

[0001] The present invention relates to a stabilized power supply-usedevice including power transistors, a control circuit of the powertransistor, and other electronic components which are formed into anintegrated circuit, and constituting a main part of the stabilized powersupply, used for a power supply for VCR (Video Cassette Recorder) use,for example, in which an input voltage is stabilized to a desiredvoltage so as to be outputted by stepping down the input voltage throughon-resistance of the power transistor or switching the power transistor,and relates to a switching power supply and an electronic device usingthe stabilized power supply-use device.

BACKGROUND OF THE INVENTION

[0002]FIG. 9 is a block diagram showing an electrical arrangement of atypical switching power supply 1 used for a power supply for VCR use,and others. The switching power supply 1 is a so-called three-terminalregulator including an input terminal P1, an output terminal P2, and anearth terminal P3, and primarily includes: an integrated circuit(hereinafter referred to IC) 2 for performing switching operation; asmoothing capacitor C1 for stabilizing an input voltage Vin andoutputting the input voltage Vin to the IC 2; a choke coil L1 forsmoothing a current switched by the IC 2; a reflux diode D1 and asmoothing capacitor C2; voltage-dividing resistors R1 and R2 fordividing a smoothed output voltage Vo to feed back to the IC 2.

[0003] The IC 2 maintains the output voltage Vo constant by switchingthe input voltage Vin supplied to a first terminal of the IC 2,outputting it from a second terminal of the IC 2 to the choke coil L1and the reflux diode D1, and changing the switching duty in accordancewith a feedback voltage Oadj fed back from a fourth terminal of the IC2. A third terminal of the IC 2 is connected to ground. A fifth terminalof the IC 2 is a terminal for detecting the rising edge of the inputvoltage Vin and is used for a soft start control as will hereinafter bedescribed.

[0004]FIG. 10 is a block diagram showing an electrical arrangement of atypical and conventional IC 11 used for the IC 2. In FIG. 10, componentscorresponding to those in FIG. 9 are given the same reference numerals.The IC 11 includes power transistors q1 and q2, a reference voltagesource (VREF) 12, an error (differential) amplifier 13, an oscillator14, a PWM (Pulse Width Modulation) comparator 15, an NOR gate 16, anovercurrent detecting resistor r11, an overcurrent detection circuit 17,an overheat detection circuit 18, an OR gate 19, a flip-flop 20, aconstant voltage circuit 21, an ON/OFF circuit 22, a soft start circuit23, a zener diode d11, and a resistor r12.

[0005] The error amplifier 13 amplifies the difference between thefeedback voltage Oadj from a fourth terminal of the IC 11 and aninternal reference voltage VREF generated in the reference voltagesource 12. The PWM comparator 15 slices a triangular wave from theoscillator 14 to generate a control switching pulse in accordance withan output voltage of the error amplifier 13. The control switching pulseis supplied via the NOR gate 16 to a base of the P-type power transistorq2 so that switching is performed in the power transistors q1 and q2.

[0006] The power transistor q2 and the N-type power transistor q1 whichis connected in series with an output line are in Darlington connection.A low level input from the NOR gate 16 to the base of the powertransistor q2 results in the power transistor q2 being on. This alsocauses the power transistor q1 to be on, and a switching pulse isoutputted from a second terminal of the IC 11. The outputted switchingpulse is supplied to a load while exciting the choke coil L1 shown inFIG. 9. On the other hand, a high level input to the base of the powertransistor q2 results in the power transistor q2 being off. This alsocauses the power transistor q1 to be off, and the switching pulse is notoutputted from the second terminal of the IC 11. Energy stored in thechoke coil L1 is released via the reflux diode D1. Then, the switchingduty is changed in accordance with the feedback voltage Oadj, therebyperforming constant voltage control to maintain the output voltage Voconstant.

[0007] Meanwhile the flip-flop 20 is reset at each oscillation cycle bya pulse from the oscillator 14. However, the flip-flop 20 is not setwhile an abnormal output is not fed from the OR gate 19, i.e. both theovercurrent detection circuit 17 and the overheat detection circuit 18,an output Q-bar (Q-bar represents the inverted output) goes high level.The NOR gate 16 inverts the switching pulse fed from the PWM comparator15 and supplies the inverted switching pulse to the base of the powertransistor q2. On the other hand, when an abnormal output is fed fromeither the overcurrent detection circuit 17 or the overheat detectioncircuit 18, the flip-flop 20 is set, and the output Q-bar goes lowlevel. The NOR gate 16 masks the switching pulse from the PWM comparator15, which stops switching of the power transistors q2 and q1.

[0008] At the next switching cycle, the flip-flop 20 is reset by a pulsefrom the oscillator 14. However, if the abnormal output from theovercurrent detection circuit 17 or the overheat detection circuit 18 isfed continuously, the switching pulse is kept masked. If the abnormaloutput is removed, the switching becomes possible. In this manner,overcurrent protection and overheat protection are carried out.

[0009] The overcurrent detecting resistor r11, which is inserted betweena first terminal of the IC 11 and a collector of the power transistorq1, is made up of aluminum wiring patterns inside the IC 11. Theovercurrent detection circuit 17 detects the occurrence of anovercurrent on the basis of whether a voltage drop across theovercurrent detecting resistor r11 is of a predetermined voltage level.

[0010] The constant voltage circuit 21 supplies a power based on theinput voltage Vin to internal circuits of the IC 11, such as the erroramplifier 13 and the PWM comparator 15. The ON/OFF circuit 22 isconnected to a fifth terminal of the IC 11 via the resistor r12. Whenthe fifth terminal goes low level, i.e. a supply of the input voltageVin is cut off, the ON/OFF circuit 22 causes the power transistors q2and q1 to be off. When the fifth terminal goes high level, i.e. theinput voltage Vin rises, the ON/OFF circuit 22 causes the powertransistors q2 and q1 to be on.

[0011] With an arrangement in which a capacitor is additionallyconnected to a zeroth terminal connected to the first terminal, to whichthe input voltage Vin is supplied, so as to prevent overshoot of theoutput voltage Vo, the soft start circuit 23 prevents overshoot of theoutput voltage Vo by comparing an output voltage from the erroramplifier 13 with a voltage of the connected capacitor increased by aconstant current outputted from the zeroth terminal at power-on and bygradually expanding a pulse width for being the power transistors q2 andq1 on. The zener diode d11 is inserted to clamp an upper limit voltageof the capacitor when the capacitor is additionally connected to thezeroth terminal.

[0012] The above-arranged IC 11 aims for integration of electroniccomponents as an IC in Japanese Laid-Open Patent application No.180806/1994 (Tokukaihei 6-180806; published on Jun. 28, 1994), andintegrates essential components making up a switching power supply, suchas the power transistor q2 and q1 and circuits for controlling the powertransistor q2 and q1. However, some switching power supplies include theIC 2 being made up of discreet components. In such a switching powersupply, an overcurrent detection capability is generally not included inthe IC 2.

[0013] The conventional IC 11 as described above is susceptible tovariations in the overcurrent detecting resistor r11 being made up ofaluminum wiring patterns. At an overload test based on a safety standardfor a power supply of a product, the conventional IC 11 is beyond asafety standard for the product, for example, 15W, as indicated byreference numerals α1-α2 in FIG. 11. When it is beyond 15W, another testis required, and it takes a lot of trouble with a test based on a safetystandard. In addition, an input power capacity must be set to be largeenough so that the switching power supply does not go down even at theupper limit power of a safety standard up to a power in an overloadedstate.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide a stabilizedpower supply-use device which can simplify a test procedure andeliminate the need for a needlessly increased input power capacity, anda switching power supply and an electronic device using the stabilizedpower supply-use device.

[0015] In order to achieve the above object, a stabilized powersupply-use device of the present invention includes: an integratedcircuit for use in stabilizing an input voltage to a predeterminedvoltage so as to output the predetermined voltage; and an element forovercurrent detection being exposed outside of the integrated circuit.

[0016] According to the above arrangement, a stabilized power supply-usedevice formed as an integrated circuit integrally includes powertransistors, a control circuit for controlling a base current and a gatevoltage of the power transistor, and other electronic components,wherein an element for overcurrent detection, which was conventionallyincluded in the integrated circuit, is exposed outside of the integratedcircuit by being connected in series with the power transistor.

[0017] Therefore, as compared to the element for overcurrent detectionbeing made up of aluminum wiring patterns, the element for overcurrentdetection of the present invention dramatically decreases elementvariations, whereby it is possible to improve an accuracy of voltagedetection and to arbitrarily set a constant for an element. This cansimplify a test procedure and eliminate the need for a needlesslyincreased input power capacity in a test based on safety standard andother tests, thereby enabling a switching power supply manufactured at alower cost.

[0018] Further, another stabilized power supply-use device of thepresent invention includes: an integrated circuit for use in stabilizingan input voltage to a predetermined voltage so as to output thepredetermined voltage by controlling a power transistor which isconnected in series with a power supply line; and an overcurrentdetecting resistor which is connected in series with the power supplyline being realized by a resistor externally provided to the integratedcircuit.

[0019] According to the above arrangement, a stabilized power supply-usedevice of the present invention, which is a semiconductor device for usein a stabilized power supply, includes a power transistor and anovercurrent detecting resistor, wherein the power transistor isconnected in series with a power supply line, on-resistance of the powertransistor being changed, or the power transistor being switched so thatan input voltage is stabilized to a predetermined voltage so as to beoutputted, and the semiconductor device being formed as an integratedcircuit in which the power transistor is integrally included with acontrol circuit for controlling the power transistor and otherelectronic components in order to obtain the predetermined voltage,wherein the overcurrent detecting resistor, which was conventionallyincluded in the integrated circuit, is provided externally.

[0020] Therefore, as compared to the overcurrent detecting resistorbeing made up of aluminum wiring patterns inside the integrated circuit,the overcurrent detecting resistor of the present invention dramaticallydecreases variations in value of resistance, whereby it is possible toimprove an accuracy of voltage detection and to arbitrarily set a valueof resistance. This eliminates the need for a needlessly increased inputpower capacity in a test based on safety standard and other tests,thereby enabling a switching power supply manufactured at a lower cost.

[0021] A switching power supply of the present invention uses theabove-described stabilized power supply-use device.

[0022] According to the above arrangement, it is possible to realize alow-cost switching power supply eliminating the need for a needlesslyincreased input power capacity in a test based on safety standard andother tests.

[0023] Still further, an electronic device of the present invention usesthe above-described switching power supply.

[0024] According to the above arrangement, for the power supply for VCRuse and other power supply, it is possible to mount a low-cost powersupply eliminating the need for a needlessly increased input powercapacity in a test based on safety standard and other tests.

[0025] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a block diagram showing an electrical arrangement of anIC according to the first embodiment of the present invention for use ina switching power supply.

[0027]FIG. 2 is a front view showing an example of a specificconfiguration of the IC shown in FIG. 1.

[0028]FIG. 3 is a block diagram showing an electrical arrangement of anIC according to the second embodiment of the present invention.

[0029]FIG. 4 is a block diagram showing an electrical arrangement of anIC according to the third embodiment of the present invention.

[0030]FIG. 5 is a block diagram showing an electrical arrangement of anIC according to the fourth embodiment of the present invention.

[0031]FIG. 6 is a block diagram showing an alternative electricalarrangement of the IC according to the fourth embodiment of the presentinvention.

[0032]FIG. 7 is a block diagram showing an electrical arrangement of anIC according to the fifth embodiment of the present invention.

[0033]FIG. 8 is a block diagram showing an electrical arrangement of anIC according to the sixth embodiment of the present invention.

[0034]FIG. 9 is a block diagram showing an electrical arrangement of atypical switching power supply used for a power supply for VCR use.

[0035]FIG. 10 is a block diagram showing an electrical arrangement of atypical and conventional IC for use in the switching power supply.

[0036]FIG. 11 is a graph showing current-voltage characteristics of aswitching power supply caused by variations in overcurrent detectingresistors in the conventional art and the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0037] The following will describe embodiments of the present inventionwith reference to FIG. 1 through FIG. 8 and FIG. 11.

First Embodiment

[0038] The following will describe the first embodiment of the presentinvention with reference to FIGS. 1, 2, and 11.

[0039]FIG. 1 is a block diagram showing an electrical arrangement of anIC 31 of the first embodiment of the present invention. The IC 31 isused for the IC 2 in the switching power supply 1 shown in FIG. 9, andin FIG. 1, components corresponding to those in FIG. 9 are given thesame reference numerals. The IC 31 includes power transistors Q1 and Q2,a reference voltage source 32, an error amplifier 33, an oscillator 34,a PWM comparator 35, an NOR gate 36, an overcurrent detecting resistorR11, an overcurrent detection circuit 37, an overheat detection circuit38, an OR gate 39, a flip-flop 40, a constant voltage circuit 41, anON/OFF circuit 42, a soft start circuit 43, a zener diode D11, and aresistor R12.

[0040] The error amplifier 33 amplifies a difference between thefeedback voltage Oadj to a fourth terminal of the IC 31 and an internalreference voltage VREF generated in the reference voltage source 32. ThePWM comparator 35 slices a triangular wave from the oscillator 34 togenerate a control switching pulse in accordance with an output voltageof the error amplifier 33. The control switching pulse is supplied viathe NOR gate 36 to a base of the P-type power transistor Q2 so thatswitching is performed in the power transistors Q1 and Q2.

[0041] The power transistor Q2 and the N-type power transistor Q1 whichis connected in series with an output line are in Darlington connection.A low level input from the NOR gate 36 to the base of the powertransistor Q2 results in the power transistor Q2 being on. This alsocauses the power transistor Q1 to be on, and a switching pulse isoutputted from a second terminal of the IC 31. The switching pulse issupplied to a load while exciting the choke coil L1. On the other hand,a high level input to the base of the power transistor Q2 results in thepower transistor Q2 being off. This also causes the power transistor Q1to be off, and the switching pulse is not outputted from the secondterminal of the IC 31. Energy stored in the choke coil L1 is releasedvia the reflux diode D1. Then, the switching duty is changed inaccordance with the feedback voltage Oadj, thereby performing constantvoltage control to maintain the output voltage Vo constant.

[0042] Meanwhile the flip-flop 40 is reset at each oscillation cycle bya pulse from the oscillator 34. The flip-flop 40 is not set while anabnormal output is not fed from the OR gate 39, i.e. both theovercurrent detection circuit 37 and the overheat detection circuit 38,an output Q-bar from the flip-flop 40 goes high level voltage. At thismoment, the NOR gate 36 where the high level voltage is inputted to oneend thereof inverts the switching pulse fed from the PWM comparator 35and supplies the inverted switching pulse to the base of the powertransistor Q2.

[0043] On the other hand, when an abnormal output is fed from either theovercurrent detection circuit 37 or the overheat detection circuit 38,the flip-flop 40 is set, and the output Q-bar goes low level. The NORgate 36 where a voltage of low level is inputted to one end thereofmasks the switching pulse from the PWM comparator 35, which stopsswitching of the power transistors Q2 and Q1.

[0044] At the next switching cycle, the flip-flop 40 is reset by a pulsefrom the oscillator 34. However, if the abnormal output from theovercurrent detection circuit 37 or the overheat detection circuit 38 isfed continuously, the switching pulse is kept masked. If the abnormaloutput is removed, the switching becomes possible. In this manner,overcurrent protection and overheat protection are carried out.

[0045] The constant voltage circuit 41 supplies a power based on theinput voltage Vin to internal circuits of the IC 31, such as the erroramplifier 33 and the PWM comparator 35. The ON/OFF circuit 42 isconnected to a fifth terminal of the IC 31 via the resistor R12. Whenthe fifth terminal goes low level, i.e. a supply of the input voltageVin is cut off, the ON/OFF circuit 42 causes the power transistors Q2and Q1 to turn off. When the fifth terminal goes into high level, i.e.the input voltage Vin rises, the ON/OFF circuit 42 causes the powertransistors Q2 and Q1 to turn on.

[0046] With an arrangement in which a capacitor is additionallyconnected to a zeroth terminal connected to the first terminal, to whichthe input voltage Vin is supplied, so as to prevent overshoot of theoutput voltage Vo, the soft start circuit 43 prevents overshoot of theoutput voltage Vo by comparing an output voltage from the erroramplifier 33 with a voltage of the connected capacitor increased by aconstant current outputted from the zeroth terminal at power-on and bygradually expanding a pulse width for being the power transistors Q2 andQ1 on. The zener diode D11 is inserted to clamp an upper limit voltageof the capacitor when the capacitor is additionally connected to thezeroth terminal. The above arrangement of the IC 31 is the same as thearrangement of the conventional IC 11 shown in FIG. 10.

[0047] Note that, in the IC 31 of the present invention, the overcurrentdetecting resistor R11 is inserted externally between a sixth terminalconnected to the first terminal to which the input voltage Vin issupplied and a seventh terminal connected to a collector of the powertransistor Q1. The overcurrent detection circuit 37 receives voltagesfrom the sixth and seventh terminals and detects the occurrence of anovercurrent on the basis of whether a voltage drop across theovercurrent detecting resistor R11 is of a predetermined voltage level.

[0048]FIG. 2 is a front view showing an example of a specificconfiguration of the above-arranged IC 31. An IC chip 44 arranged asshown in FIG. 1 is fixed on the lead frame 45 by die bonding, and thenis interconnected by wire bonding to lead terminals 46 corresponding tothe first through seventh terminals respectively indicated by referencenumerals (1) through (7). Thereafter, the overcurrent detecting resistorR11 consisting of chip components is mounted between lead terminalsrespectively corresponding to the sixth and seventh terminals, and thensealed hermetically by a mold resin 47.

[0049] As compared to the overcurrent detecting resistor r11 being madeup of aluminum wiring patterns, the overcurrent detecting resistor R11being made up of chip components dramatically decreases elementvariations, whereby it is possible to improve an accuracy of voltagedetection and to arbitrarily set a constant for a element. This cansimplify a test procedure and eliminate the need for a needlesslyincreased input power capacity in a test based on safety standard andother tests, thereby enabling a switching power supply manufactured at alower cost.

[0050] In FIG. 11, current-voltage characteristic caused by thevariations in the present invention is indicated by reference numeralα3. The variations in the present invention are surely reduced within15W, which is a power rating of the switching power supply. Therefore,another test is not required in the current-voltage characteristic test,and it is possible simplify a test procedure as described above.

Second Embodiment

[0051] The following will describe the second embodiment of the presentinvention with reference to FIG. 3.

[0052]FIG. 3 is a block diagram showing an electrical arrangement of anIC 51 of the second embodiment of the present invention. The IC 51 issimilar to the above-described IC 31. Components corresponding to thosein the IC 31 are given the same reference numerals, and explanationsthereof are omitted.

[0053] Note that, in the IC 51, a P-type power transistor Q1 a insertedin series with a power supply line is provided with multi-emitteroutputs. The overcurrent detecting resistor R11 is provided on theemitter side of the power transistor Q1 a, and a terminal A on alarge-current output of the power transistor Q1 a is directly connectedto a second terminal of the IC 51, which is an output terminal. Aterminal B on a small-current (e.g. as small as {fraction (1/1000)} ofthe current carried on the terminal A of the large-current output)output of the power transistor Q1 a is connected to one terminal of theovercurrent detecting resistor R11 via a sixth terminal, and a seventhterminal which is connected to the other terminal of the overcurrentdetecting resistor R11 is connected to the second terminal, which is anoutput terminal.

[0054] Therefore, different from the power transistor Q1 outputting afull-load current to the overcurrent detecting resistor R11, the powertransistor Q1 a divides the full-load current into a small current and alarge current. The small current is taken outside of the IC 51 so as tobe outputted to the overcurrent detecting resistor R11, so that it ispossible to reduce power consumed by the overcurrent detecting resistorR11.

Third Embodiment

[0055] The following will describe the third embodiment of the presentinvention with reference to FIG. 4.

[0056]FIG. 4 is a block diagram showing an electrical arrangement of anIC 61 of the third embodiment of the present invention. The IC 61 issimilar to the above-described IC 51. Components corresponding to thosein the IC 51 are given the same reference numerals, and explanationsthereof are omitted. Note that, the IC 61 replaces the power transistorsQ1 and Q2 with a power MOSFET (Metal Oxide Semiconductor Field EffectTransistor) Q12 with a current-sense capability. A sense terminal B ofthe power MOSFET Q12 is connected to one terminal of the overcurrentdetecting resistor R11 via a sixth terminal, and a seventh terminalwhich is connected to the other terminal of the overcurrent detectingresistor R11 is connected to a second terminals, which is an outputterminal. A low active switching pulse from the NOR gate 36 is suppliedto the gate of the P-type power MOSFET Q12.

[0057] Therefore, as the power transistor Q1 a, the power MOSFET Q12does not output a full-load current to the overcurrent detectingresistor R11, but outputs a minute current proportional to a loadcurrent carried on the sense terminal B to the overcurrent detectingresistor R11, so that it is possible to reduce power consumed by theovercurrent detecting resistor R11.

Fourth Embodiment

[0058] The following will describe the fourth embodiment of the presentinvention with reference to FIGS. 5 and 6.

[0059]FIG. 5 is a block diagram showing an electrical arrangement of anIC 71 of the fourth embodiment of the present invention. FIG. 6 is ablock diagram showing an electrical arrangement of an IC 81 which is analternative example of the fourth embodiment of the present invention.The ICs 71 and 81 are similar to the above-described IC 31. Componentscorresponding to those in the IC 31 are given the same referencenumerals, and explanations thereof are omitted.

[0060] Note that, in the ICs 71 and 81, a lead terminal is used both asone of a pair of lead terminals, which are necessary to provide theovercurrent detecting resistor R11 externally as described above, and aninput or output terminal.

[0061] That is, in the IC 71 shown in FIG. 5, one terminal of theovercurrent detecting resistor R11 is connected to a first terminal,which is an input terminal, and the other terminal is connected to asixth terminal which is an input terminal of the input voltage Vin.Therefore, the seventh terminal connected to the collector of the powertransistor Q1 in the IC 31 of FIG. 1 is omitted in the IC 71.

[0062] Meanwhile, in the IC 81 shown in FIG. 6, the overcurrentdetecting resistor R11 is inserted on an emitter side of the powertransistor Q1. One terminal of the overcurrent detecting resistor R11 isconnected to a second terminal, which is an output terminal, and theother terminal is a sixth terminal, which is an output terminal of theoutput voltage Vo. Therefore, the seventh terminal in the IC 31 of FIG.1 is omitted in the IC 81. In this manner, the number of lead terminalscan be decreased.

Fifth Embodiment

[0063] The following will describe the fifth embodiment of the presentinvention with reference to FIG. 7.

[0064]FIG. 7 is a block diagram showing an electrical arrangement of anIC 91 of the fifth embodiment of the present invention. The IC 91 issimilar to the above-described IC 31. Components corresponding to thosein the IC 31 are given the same reference numerals, and explanationsthereof are omitted. Note that, in the IC 91, on the basis of the factthat the overcurrent detecting resistor is provided externally andexposed outside of the IC 91, an overcurrent detecting resistor R11 a isrealized by a variable resistor such as a semi-fixed resistor.

[0065] Therefore, a resistance value can be adjusted readily.

Sixth Embodiment

[0066] The following will describe the sixth embodiment of the presentinvention with reference to FIG. 8. FIG. 8 is a block diagram showing anelectrical arrangement of an IC 101 of the sixth embodiment of thepresent invention. The IC 101 is similar to the above-described IC 31.

[0067] Note that, the IC 101 includes a temperature compensation circuit102 having a temperature characteristic approximately equal to that ofthe overcurrent detecting resistor R11 which is provided externally. Aresult of the detection by the overcurrent detecting resistor R11 iscompensated by the temperature compensation circuit 102 and inputted tothe overcurrent detection circuit 37.

[0068] Therefore, change in resistance value of the overcurrentdetecting resistor R11 with a temperature change is compensated by thetemperature compensation circuit 102 inside the IC 101, so that it ispossible to maintain a constant accuracy of current detection againsttemperature changes and to further suppress the above-described increasein the input power capacity.

[0069] Further, it is obvious that the sixth embodiment is applicable toall of the second through fifth embodiments.

[0070] The above description is given based on a switching power supplywhich causes the power transistor Q1, Q1 a, or Q12 to switch so that theinput voltage Vin is stabilized to the desired output voltage Vo so asto be outputted. The invention is also applicable to a step-down powersupply in which the power transistor Q1, Q1 a, or Q12 is connected inseries with a power supply line, and on-resistance of the powertransistor Q1, Q1 a, or Q12 is caused to change.

[0071] As described above, a stabilized power supply-use device of thepresent invention formed as an integrated circuit integrally includespower transistors, a control circuit for controlling a base current anda gate voltage of the power transistor, and other electronic components,and an element for overcurrent detection, which was conventionallyincluded in the integrated circuit, is exposed outside of the integratedcircuit by being connected in series with the power transistor.

[0072] Therefore, as compared to the element for overcurrent detectionbeing made up of aluminum wiring patterns, the element for overcurrentdetection of the present invention dramatically decreases elementvariations, whereby it is possible to improve an accuracy of voltagedetection and to arbitrarily set a constant for an element. This cansimplify a test procedure and eliminate the need for a needlesslyincreased input power capacity in a test based on safety standard andother tests, thereby enabling a switching power supply manufactured at alower cost.

[0073] Further, as described above, a stabilized power supply-use deviceof the present invention, which is a semiconductor device for use in astabilized power supply, may comprise a power transistor and anovercurrent detecting resistor, wherein the power transistor is a powertransistor and is connected in series with a power supply line,on-resistance of the power transistor being changed, or the powertransistor being switched so that an input voltage is stabilized to apredetermined voltage so as to be outputted, and the semiconductordevice being formed as an integrated circuit in which the powertransistor is integrally included with a control circuit for controllingthe power transistor and other electronic components in order to obtainthe predetermined voltage wherein the overcurrent detecting resistor,which was conventionally included in the integrated circuit, is providedexternally.

[0074] Therefore, as compared to the overcurrent detecting resistorbeing made up of aluminum wiring patterns inside the integrated circuit,the overcurrent detecting resistor of the present invention dramaticallydecreases variations in value of resistance, whereby it is possible toimprove an accuracy of voltage detection and to arbitrarily set a valueof resistance. This eliminates the need for a needlessly increased inputpower capacity in a test based on safety standard and other tests,thereby enabling a switching power supply manufactured at a lower cost.

[0075] Still further, as described above, a stabilized power supply-usedevice of the present invention may include a power transistor withmulti-emitter, as the power transistor, which does not output afull-load current to the overcurrent detecting resistor, but divides thefull-load current into a small current and a large current, and takesthe small current outside and outputs it to the overcurrent detectingresistor.

[0076] Therefore, it is possible to reduce power consumed by theovercurrent detecting resistor.

[0077] Further, as described above, a stabilized power supply-use deviceof the present invention may include a power MOSFET with a current-sensecapability as the power transistor which does not output a full-loadcurrent to the overcurrent detecting resistor, but takes outside aminute current proportional to a load current carried on the senseterminal so as to output it to the overcurrent detecting resistor.

[0078] Therefore, it is possible to reduce power consumed by theovercurrent detecting resistor.

[0079] Still further, as described above, a stabilized power supply-usedevice of the present invention may include a lead terminal used both asone terminal of the overcurrent detecting resistor and an input oroutput terminal. Therefore, the number of lead terminals can bedecreased.

[0080] Further, as described above, a stabilized power supply-use deviceof the present invention may include an overcurrent detecting resistorrealized by a variable resistor on the basis of the fact that theovercurrent detecting resistor is provided externally and exposedoutside of the integrated circuit. Therefore, a resistance value can beadjusted readily.

[0081] Still further, as described above, a stabilized power supply-usedevice of the present invention may include a temperature compensationcircuit having a temperature characteristic approximately equal to thatof the overcurrent detecting resistor externally provided in theintegrated circuit.

[0082] Therefore, change in resistance value of the overcurrentdetecting resistor, which provided externally and exposed outside of theintegrated circuit, with a temperature change is compensated by thetemperature compensation circuit in a control circuit inside theintegrated circuit, so that it is possible to maintain a constantaccuracy of current detection and to further suppress theabove-described increase in the input power capacity.

[0083] Further, as described above, a switching power supply of thepresent invention includes the above-described stabilized powersupply-use device.

[0084] Therefore, it is possible to realize a low-cost switching powersupply eliminating the need for a needlessly increased input powercapacity in a test based on safety standard and other tests.

[0085] Still further, as described above, an electronic device of thepresent invention includes the above-described switching power supply.

[0086] Therefore, for the power supply for VCR use and other powersupply, it is possible to mount a low-cost power supply eliminating theneed for a needlessly increased input power capacity in a test based onsafety standard and other tests.

[0087] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe included within the scope of the following claims.

What is claimed is:
 1. A stabilized power supply-use device, comprising:an integrated circuit for use in stabilizing an input voltage to apredetermined voltage so as to output the predetermined voltage; and anelement for overcurrent detection being provided to be exposed outsideof the integrated circuit.
 2. A stabilized power supply-use device,comprising: an integrated circuit for use in stabilizing an inputvoltage to a predetermined voltage so as to output the predeterminedvoltage by controlling a power transistor which is connected in serieswith a power supply line; and an overcurrent detecting resistor which isconnected in series with the power supply line being realized by aresistor externally provided to the integrated circuit.
 3. Thestabilized power supply-use device according to claim 2, wherein: thepower transistor is a transistor with multi-emitter outputs, and theovercurrent detecting resistor is connected to a small-current output ofthe multi-emitter outputs.
 4. The stabilized power supply-use deviceaccording to claim 2, wherein: the power transistor is realized by apower MOSFET with current-sense capability, and the overcurrentdetecting resistor is connected to a sense terminal of the power MOSFET.5. The stabilized power supply-use device according to claim 2, wherein:a lead terminal is used both as one terminal of the overcurrentdetecting resistor and an input or output terminal.
 6. The stabilizedpower supply-use device according to claim 2, wherein: the overcurrentdetecting resistor is a variable resistor.
 7. The stabilized powersupply-use device according to claim 2, wherein: the integrated circuitincludes a temperature compensation circuit having a temperaturecharacteristic approximately equal to that of the overcurrent detectingresistor externally provided.
 8. A switching power supply including astabilized power supply-use device which comprises: an integratedcircuit for use in stabilizing an input voltage to a predeterminedvoltage so as to output the predetermined voltage; and an element forovercurrent detection being provided to be exposed outside of theintegrated circuit.
 9. A switching power supply including a stabilizedpower supply-use device which comprises: an integrated circuit for usein stabilizing an input voltage to a predetermined voltage so as tooutput the predetermined voltage by controlling a power transistor whichis connected in series with a power supply line; and an overcurrentdetecting resistor which is connected in series with the power supplyline being realized by a resistor externally provided to the integratedcircuit.
 10. An electronic device including a switching power supplyhaving a stabilized power supply-use device which comprises: anintegrated circuit for use in stabilizing an input voltage to apredetermined voltage so as to output the predetermined voltage; and anelement for overcurrent detection being provided to be exposed outsideof the integrated circuit.
 11. An electronic device including aswitching power supply having a stabilized power supply-use device whichcomprises: an integrated circuit for use in stabilizing an input voltageto a predetermined voltage so as to output the predetermined voltage bycontrolling a power transistor which is connected in series with a powersupply line; and an overcurrent detecting resistor which is connected inseries with the power supply line being realized by a resistorexternally provided to the integrated circuit.